US scientists studying links between genes and scouting behavior in bees have discovered some intriguing similarities in human and insect novelty-seeking behaviour that suggests the trait, which is assumed to have evolved separately in these lineages, may share some genetic components. Gene Robinson, an entomologist and geneticist at the University of Illinois, Urbana-Champaign, and colleagues report their findings in the 9 March online issue of Science.
They begin their report by saying we know little about the molecular basis of the differences in behavior among individuals.
One behavior that interests many scientists that study insects, is that of honey bee scouts. Unlike many foragers, they don’t wait to be told where to go, they are the intrepid pioneers of honeybee societies.
“Scouts go out and search for food on their own,” Robinson told ScienceNOW. They also look for new nest sites.
In bee societies, scouts are females that constantly search for new food sources. When they find one, they fly back to the colony, and communicate their news by performing the famous “waggle dance”. They then show no more interest in the new discovery, and fly off again, on a new mission.
For this study, Robinson and colleagues compared differences between scout bees and foragers that do not scout.
They identified scout bees in a colony by placing a hive in a large outdoor cage enclosed with mesh that the bees could not penetrate. They placed a food source outside the hives, and let the bees became used to it.
Then one day, they introduced an alternative food source in another part of the enclosure, and watched while bees “discovered” it. They marked these bees by dabbing a touch of paint on their bodies. The color of the paint identified the new food source.
The researchers repeated this on the next day, with a second alternative food source. Again they waited for the bees to find it, and marked them with yet a different color.
On the third day, they introduced a third alternative food source, and again, marked the bees that found it with a third unique color.
Thus, it was possible for a scout bee to end up with three different colored spots on her body. The researchers defined a scout bee as one that had at least two such colored spots, indicating she had visited at least two new food sources.
At the end of the experiment, the researchers captured the bees that visited the food sources. Some of them were scouts (with two or more different colored dots), and the others were non-scouts or foragers.
They removed the brains from the captured bees and compared the patterns of gene expression between scouts and non- scouts.
They found significant differences in gene expression in about 16% of the 7,500 genes in both types of bee.
They compared these results with what is already known from extensive research in verterbrates, including humans, and discovered that several of the genes whose expression was unique in the scout bees were also those linked to novelty-seeking in vertebrates. These included some for receptors of the neurotransmitters dopamine and glutamate, both of which exist in humans too.
In a final phase of their study, Robinson and colleagues tested what happened when they gave the non-scouting bees the “missing ingredients”.
When the researchers gave glutamate to the non-scouting forager bees, they were more likely to search for food when their hive was relocated in a new enclosure. Giving them a glutamate inhibitor at the same time stopped their searching behavior.
When the researchers gave them octopamine, a chemical that activates the dopamine receptor, it had the same effect: the non-scouting bees started showing scouting behaviors.
The researchers concluded that novelty-seeking behavior in vertebrates like humans, and insects like bees, have the same or similar genetic components.
This is intriguing because humans and bees are by no means close on the family tree of living things. If you go back far enough along the branches, the common ancestor is probably a kind of marine flatworm, says Robinson, and the chances of that species having scouts are practically zero.
Robinson says their findings raise the possibility that the same group of genetic molecular components has produced similar behaviors at different points of evolution.
Written by Catharine Paddock PhD